1. Field of the Invention
The present invention relates to a torque limiter and a drive device.
2. Description of the Related Art
Toilets equipped with an electrically powered toilet seat/lid opening and closing function that each include a drive unit to automatically open and close a toilet seat or a toilet lid are commercially available. A drive unit for such a function includes a torque limiter in order that a gear and a motor included in the drive unit may be protected when a person applies an excess load to a toilet seat or a toilet lid by manually opening and closing the toilet seat or the toilet lid. As such a torque limiter, one including a ratchet has been proposed (see Patent Literature 1).
In a torque limiter disclosed in Patent Literature 1 (Japanese Patent Application Laid-open No. 2014-149013), upon application of an excess load exceeding previously determined torque (certain torque) to a toilet seat or a toilet lid when the toilet seat or the toilet lid is opened or closed, ratchet elements that have been engaged become disengaged, so that transmission of the excess load is shut off. Disadvantageously, however, rotation of the ratchet elements then causes mechanical noise. If the certain torque is set relatively high for the purpose of suppressing the frequencies of occurrences of such mechanical noise, peripheral components such as a motor and a gear need to have sufficiently high strength so as to be tolerable against at least an excess load that does not exceed the certain torque, and the component costs increase by satisfying such need. Furthermore, in the case of a ratchet made of resin, large variations are seen in torque (limit torque) at which transmission of excess loads is actually shut off, and the variations in limit torque may become larger over time because the ratchet itself deforms when rotating.
Problems similar to the above occur when the torque limiter is used for automatically opening and closing any movable objects other than a toilet seat.
The present invention has been made in view of the above situation, and is aimed at providing a torque limiter and a drive device that are capable of suppressing influence of an excess load to components thereof and silently operable.